Why Unity android app loading too slow - How to check

I have develop an app with unity 5.2 for Android platform. The app is running perfectly but its loading time is about 7 to 10 seconds at-least. Unity splash screen display for at least 7 seconds in my s5 phone. My app first scene that taking time in loading contains 6 Canvas for different UI purposes. It is mandatory for me to retain these 6 canvas as i have code already. I can't go back from here.

So my question is that how can I debug APK to know that which thing taking to much time? Remeber my scene first scene don't contains any models accept two simple object .